Edge emitting semiconductor lasers for high output powers are usually embodied as broad stripe laser, in which the active region has a width of approximately 100 μm or more. Owing to the comparatively large lateral extent of the active region, generally a large number of lateral laser modes can establish oscillation in the case of semiconductor lasers of this type. In the case of high light powers, in particular, an undesired high degree of modulation of the light power can occur, which is also referred to as filamenting. In the case of edge emitting semiconductor lasers, the maximum output power density is limited by melting of the semiconductor body in the region of the side facets, which is also referred to as COMD (catastrophic optical mirror damage). As a result, the maximum possible output power is reduced in the case of a semiconductor laser having a high degree of filamenting. Furthermore, multimode operation of an edge emitting semiconductor laser makes it more difficult to couple the emitted laser light into downstream optical elements, in particular, into optical waveguides.
In order to suppress higher lateral laser modes, in particular, in order to obtain operation in the lateral fundamental mode, the document WO 01/97349 A1 discloses forming phase structures in the waveguide of an edge emitting semiconductor laser. The phase structures are regions of the semiconductor body in which the effective refractive index deviates from the effective refractive index of the regions of the semiconductor body that adjoin in a lateral direction and which are formed such that higher laser modes incur greater circulation losses in the laser resonator than the lateral fundamental mode of the semiconductor laser. In the case of an edge emitting semiconductor laser in which the active layer is arranged between two waveguide layers and the waveguide layers are arranged between two cladding layers, the phase structure is produced, for example, by the waveguide being thinned right into the region of a waveguide layer. What is achieved in this way, for example, is that the effective refractive index for the laser radiation propagating in a lateral direction is smaller by Δn=0.03 in the thinned region than in the non-thinned region.